Flexible couplings are employed to accommodate axial misalignment of two shafts connected to the coupling and are typically used in tapping and drilling operations to facilitate the proper positioning of the tap or drill tool with respect to the work surface. A flexible coupling allows a tool shaft to shift out of axial alignment with a drive shaft and shift into axial alignment with a preformed opening for reaming or tapping. In addition, a flexible coupling facilitates the drilling of new holes by enabling alignment of a drill to be normal to a work surface that is inclined with respect to a drive shaft.
Typical prior art flexible couplings utilize some form of universal joint to which the drive shaft and the tool shaft are attached. The universal joint permits rotation of the shafts when they are axially misaligned. In some cases, the joint is enclosed by a resilient body, such as rubber. The resilient body resists deflection of the joint and returns the misaligned shafts into axial alignment when the tool is not engaged with the work surface. While prior art flexible couplings have generally served their intended purpose, they have several disadvantages.
One disadvantage is the inability of the prior art couplings to repeatedly engage and disengage a series of tool shafts as the coupling and the drive shaft are rotating. This inability prevents a robotically positioned drive motor from automatically engaging and disengaging the various tool shafts as the drive motor is rotating. Instead, the drill motor must be stopped and the tools must be manually exchanged. In addition, prior art flexible couplings do not have the ability to automatically engage and disengage tool shafts of different size diameters, thus limiting the application of robotically controlled drive motors.
A further disadvantage of many prior art couplings is their inability to take a thrust load without compressing. In other words, couplings that utilize a resilient cushion or sleeve to connect the drive shaft and the tool shaft will compress when a thrust load is applied by the drive shaft. As a result of this compression, the depth of thrust of the tool shaft will be less than that of the drive shaft, thus limiting the application of robotically controlled drive motors have preprogrammed depth of thrust.
Another disadvantage is the inability to adjust the amount of resilient force exerted by the enclosing resilient body on the universal joint to compensate for resilient body wear and loss of resiliency or the attachment of a heavy tool to the universal joint. The inability to adjust the amount of resilient force results in the resilient body being unable to return the tool shaft and the drive shaft to axial alignment. As a result, the tool shaft will not be in alignment for the next operation, possibly causing damage or inaccurate machining. This drawback necessitates frequent replacement of the coupling, resulting in costly delays.